1. Field of the Invention
This invention relates to dental compositions containing metal complexed ascorbic acid. More specifically, it relates to curable dental compositions containing metal complexed ascorbic acid.
2. Description of the Background Art
Ascorbic acid (i.e., vitamin C) is a well known natural reducing agent or antioxidant. It has been utilized in combination with an oxidizing agent in nonaqueous dental systems. However, it is well recognized that ascorbic acid is easily oxidized, especially in aqueous solution, and in its oxidized or partially oxidized form exhibits a yellow to yellow/brown coloration.
Metal complexes of ascorbic acid have been prepared and characterized. Jabs et al. in Z. Anorg. Allg. Chem. (1984), Vol. 514, p. 179-184 describe the synthesis of ascorbate complexes of some metals of the first transition series (e.g., TiO.sup.2+, Cr.sup.3+, Mn.sup.2+, Co.sup.2+ Ni.sup.2+ and Zn.sup.2+) to study the biochemical mechanism of metal ion catalyzed autooxidation of pharmaceutical and naturally occurring vitamin C. The specific complexes discussed (i.e., TiO.sup.2+ Ni.sup.2+) were highly colored compounds.
Jabs et al. in Z. Anorg. Allg. Chem. (1984), Vol. 514, p. 185-195 report the electronic, infrared and .sup.1 H nuclear magnetic resonance spectral characterization of titanyl ascorbates.
Jabs et al. in Inorganica Chimica Acta (1990), Vol. 175 p. 273-276 describe the formation of complexes of dianions when titanium(IV) halogen compounds are independently reacted with the monoalkali and dialkali metal salts of L(+)-ascorbic acid and 5,6-O-isopropylidene-L-ascorbic acid.
Tajimir-Riahi in Journal of Inorganic Biochemistry (1991), vol. 44, p. 39-45 report the Fourier Transform infrared and .sup.13 C nuclear magnetic resonance spectroscopic analysis of Ai(III), La(VI) and Pb(II) ascorbates as solids and in solution.
Ascorbic acid in its complexed form has been prepared for use in medicinal and cosmetic compositions. Complexed ascorbic acid has also been incorporated in dental compositions to inhibit the formation and growth of calculus on tooth enamel.
U.S. Pat. Nos. 3,898,243 and 3,954,989 to Mecca disclose allantoin ascorbic acid complexes for use in medicinal and cosmetic compositions. The complexes are white powders and are reported to be stable in dry form and solutions and are not sensitive to heat.
U.S. Pat. No. 4,211,712 to Marstrand discloses a compound which comprises a complex combination of ascorbic acid, trivalent titanium and divalent copper. The complex compound is a brown solid used to treat diseases which present an abnormal blood picture.
U.S. Pat. No. 5,094,842 to Riley discloses oral compositions such as toothpastes which contain Vitamin C or a derivative thereof and a copper compound such as copper sulphate. Various alkali metal and alkaline earth metal salts are listed as suitable ascorbic acid derivatives. When the compositions further contain a stannous compound, they are reported to exhibit a reduced tendency to discolor upon storage and exposure to air.
U.S. Pat. No. 5,028,412 to Putt et al. discloses anti-calculus oral compositions that include an aluminum salt and an aliphatic carboxylic acid or salt thereof that is capable of complexing with the aluminum. Ascorbic acid is listed, along with other carboxylic acids, as a stable preferred complexing carboxylic acid. The compositions are reported to inhibit the formation and growth of calculus on dental enamel.